The sniper, perched in a window of a nearby house, hit the 75-year-old Usoyan with a single bullet as he was walking out of the Karetny Dvor restaurant in Moscow's fashionable Arbat district with bodyguards, Komsomolskaya Pravda reported.

A 33-year-old female bystander was also hit in the chest and hip in the melee and was hospitalized in serious condition.

The Russian newspaper said investigators found six 9mm shell casings in the stairwell between the fifth and sixth floors of an apartment building opposite the restaurant.

It quoted a source with the Investigative Committee of the Russian Federation as saying the sniper used a VAL assault rifle popular with Russian special forces.

"Usoyan was taken to Botkin Hospital in deep coma, unconscious, but was still breathing, and his heart was beating," a hospital source told Interfax, RT news reported. He died 10 minutes later in the hospital's emergency surgery room, the source added.

It was at least the third assassination attempt on Usoyan, RT news reported.

Usoyan, an ethnic Kurd, came from a caste of professional criminals who sport elaborate tattoos, follow unwritten prison laws codified in Stalinist-era Gulags and have been romanticized in countless popular songs, the Associated Press reported.

Komsomolskaya Pravda said Usoyan, who was involved in illegal gambling, arms and drug trafficking, and the theft of natural resources, was elected the new "godfather" of the Russian underworld following the assassination last October of crime boss Vyacheslav Ivankov, nicknamed "Yaponchik."

A would-be killer missed Usoyan in Sochi in 1998. He was seriously injured in a 2010 Moscow shooting that also hit his bodyguard.

A police source told Interfax that the 2010 and 2013 shooting appeared to be organized by the same group.

Since 2006, Usoyan had been at war with a criminal group headed by a Georgian, Tariel Oniani, the AP reported.

Usoyan was first jailed in the then-Soviet Republic of Georgia at the age of 19 for fighting police, RT news reported.

He acquired the status of "thief in law," which refers to the elite of the Soviet and post-Soviet criminal underworld, while serving time in jail from 1966 to 1968.